Method for forming package structure with a barrier layer

ABSTRACT

A method for forming a package structure includes forming an under bump metallization (UBM) layer over a metal pad and forming a photoresist layer over the UBM layer. The method further includes patterning the photoresist layer to form an opening in the photoresist layer. The method also includes forming a first bump structure over the first portion of the UBM layer. The first bump structure includes a first barrier layer over a first pillar layer. The method includes placing a second bump structure over the first bump structure. The second bump structure includes a second barrier layer over a second pillar layer. The method further includes reflowing the first bump structure and the second bump structure to form a solder joint between a first inter intermetallic compound (IMC) and a second IMC.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 16/194,927, filed Nov. 19, 2018, which claims the benefit of U.S.Provisional Application No. 62/598,594, filed on Dec. 14, 2017, theentirety of which are incorporated by reference herein.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cell phones, digital cameras, and otherelectronic equipment. Semiconductor devices are typically fabricated bysequentially depositing insulating or dielectric layers, conductivelayers, and semiconductive layers of material over a semiconductorsubstrate, and patterning the various material layers using lithographyto form circuit components and elements thereon. Many integratedcircuits are typically manufactured on a single semiconductor wafer, andindividual dies on the wafer are singulated by sawing between theintegrated circuits along a scribe line. The individual dies aretypically packaged separately, in multi-chip modules, for example, or inother types of packaging.

New packaging technologies, such as package on package (PoP), have begunto be developed, in which a top package with a device die is bonded to abottom package, with another device die. By adopting these new packagingtechnologies, various packages with different or similar functions canbe integrated together.

Although existing package structures and methods of fabricating packagestructures have generally been adequate for their intended purposes,they have not been entirely satisfactory in all respects.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It shouldbe noted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A-1H show cross-sectional representations of various stages offorming a first bump structure, in accordance with some embodiments ofthe disclosure.

FIG. 1G′ shows a cross-sectional representation of a first bumpstructure, in accordance with some embodiments of the disclosure.

FIGS. 2A-2G show top views of the conductive pad and the dielectriclayer taken along A-A′ line of FIG. 1A, in accordance with someembodiments of the disclosure.

FIG. 3A shows a cross-sectional representation of a first bumpstructure, in accordance with some embodiments of the disclosure.

FIG. 3A′ shows a cross-sectional representation of a first bumpstructure after the reflow process, in accordance with some embodimentsof the disclosure.

FIG. 3B shows a cross-sectional representation of a first bumpstructure, in accordance with some embodiments of the disclosure.

FIG. 3C shows a cross-sectional representation of a first bumpstructure, in accordance with some embodiments of the disclosure.

FIGS. 4A-4C show cross-sectional representations of various stages offorming a package structure, in accordance with some embodiments of thedisclosure.

FIG. 4C′ shows a cross-sectional representation of a package structure,in accordance with some embodiments of the disclosure.

FIGS. 5A-5J show cross-sectional representations of various stages offorming a package structure, in accordance with some embodiments of thedisclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the subject matterprovided. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Some variations of the embodiments are described. Throughout the variousviews and illustrative embodiments, like reference numbers are used todesignate like elements. It should be understood that additionaloperations can be provided before, during, and after the method, andsome of the operations described can be replaced or eliminated for otherembodiments of the method.

Other features and processes may also be included. For example, testingstructures may be included to aid in the verification testing of the 3Dpackaging or 3DIC devices. The testing structures may include, forexample, test pads formed in a redistribution layer or on a substratethat allows the testing of the 3D packaging or 3DIC, the use of probesand/or probe cards, and the like. The verification testing may beperformed on intermediate structures as well as the final structure.Additionally, the structures and methods disclosed herein may be used inconjunction with testing methodologies that incorporate intermediateverification of known good dies to increase the yield and decreasecosts.

Embodiments for a package structure and method for forming the same areprovided. FIGS. 1A-1H show cross-sectional representations of variousstages of forming a first bump structure 100 a, in accordance with someembodiments of the disclosure.

As shown in FIG. 1A, a substrate 102 is provided. The substrate 102 maybe made of silicon (Si) or another semiconductor material, such asgermanium (Ge). In some embodiments, the substrate 102 is a substrate ofa device die. In some embodiments, the substrate 102 is made of acompound semiconductor such as silicon carbide, gallium arsenic, indiumarsenide, or indium phosphide. In some embodiments, the substrate 102 ismade of semiconductor material, ceramic material, polymer material,metal material, another applicable material or a combination thereof. Insome embodiments, the substrate 102 is a glass substrate. In someembodiments, the substrate 102 is a semiconductor substrate, such assilicon wafer.

The device elements 104 are formed on substrate 102. The device elements104 include transistors (e.g., metal oxide semiconductor field effecttransistors (MOSFET), complementary metal oxide semiconductor (CMOS)transistors, bipolar junction transistors (BJT), high-voltagetransistors, high-frequency transistors, p-channel and/or n channelfield effect transistors (PFETs/NFETs), etc.), diodes, and/or otherapplicable elements. Various processes are performed to form deviceelements 104, such as deposition, etching, implantation,photolithography, annealing, and/or other applicable processes. In someembodiments, device elements 104 are formed in the substrate 102 in afront-end-of-line (FEOL) process.

The substrate 102 may include various doped regions such as p-type wellsor n-type wells). Doped regions may be doped with p-type dopants, suchas boron or BF₂, and/or n-type dopants, such as phosphorus (P) orarsenic (As). The doped regions may be formed in or on the substrate102, in a P-well structure, in an N-well structure, or in a dual-wellstructure.

The substrate 102 may further include isolation features (not shown),such as shallow trench isolation (STI) features or local oxidation ofsilicon (LOCOS) features. Isolation features may define and isolatevarious device elements.

A conductive pad 122 is formed over the ILD layer 110, and a dielectriclayer 120 is formed over the ILD layer 110 and the conductive pad 122.The dielectric layer 120 is patterned to form a recess to expose theconductive pad 122. The patterning process includes a photolithographyprocess and an etching process. Examples of a photolithography processinclude soft baking, mask aligning, exposure, post-exposure baking,developing the photoresist, rinsing and drying (e.g., hard baking). Theetching process may be a dry etching or a wet etching process. Theconductive pad 122 is electrically connected to the device elements 104through various metallic lines and vias in the dielectric layer 110.

The dielectric layer 120 is made of silicon oxide (SiOx), siliconnitride (SixNy), silicon oxynitride (SiON), dielectric material(s) withlow dielectric constant (low-k), or combinations thereof. In someembodiments, the dielectric layer 120 is made of an extreme low-k (ELK)dielectric material with a dielectric constant (k) less than about 2.5.In some embodiments, ELK dielectric materials include carbon dopedsilicon oxide, amorphous fluorinated carbon, parylene, benzocyclobutene(BCB), polytetrafluoroethylene (PTFE) (Teflon), or silicon oxycarbidepolymers (SiOC). In some embodiments, ELK dielectric materials include aporous version of an existing dielectric material, such as hydrogensilsesquioxane (HSQ), porous methyl silsesquioxane (MSQ), porouspolyarylether (PAE), porous SiLK, or porous silicon oxide (SiO₂). Insome embodiments, the dielectric layer 120 is deposited by a plasmaenhanced chemical vapor deposition (PECVD) process or by a spin coatingprocess.

The dielectric layer 120 and the conductive pad 122 are formed in aback-end-of-line (BEOL) process. The conductive pad 122 can be made ofcopper (Cu), copper alloy, aluminum (Al), aluminum alloy, tungsten (W),tungsten alloy, titanium (Ti), titanium alloy, tantalum (Ta) or tantalumalloy. In some embodiments, the conductive pad 122 is formed by aplating method.

Next, as shown in FIG. 1B, a under bump metallurgy (UBM) layer 130 isformed over the conductive pad 122 and the dielectric layer 120, inaccordance with some embodiments of the disclosure.

The UBM layer 130 may be made of conductive material, such as copper(Cu), copper alloy, aluminum (Al), aluminum alloy, tungsten (W),tungsten alloy, titanium (Ti), titanium alloy, tantalum (Ta) or tantalumalloy. In addition, the UBM layer 130 may contain an adhesion layerand/or a wetting layer. In some embodiments, the UBM layer 130 furtherincludes a copper seed layer. In some embodiments, the UBM layer 130includes an adhesion layer made of Ti/Cu and a wetting layer made of Cu.

Next, as shown in FIG. 1C, a photoresist layer 135 is formed over theUBM layer 130, in accordance with some embodiments of the disclosure.

Afterwards, as shown in FIG. 1D, the photoresist layer 135 is patternedto form an opening 137 in the photoresist layer 135, in accordance withsome embodiments of the disclosure. As a result, a portion of the UBMlayer 130 is exposed by the opening 137.

Next, as shown in FIG. 1E, a first pillar layer 142, a first barrierlayer 144 and a first solder layer 148 are sequentially formed in theopening 137, in accordance with some embodiments of the disclosure.

The first pillar layer 142 and the first barrier layer 144 are made ofdifferent materials. In some embodiments, the first pillar layer 142 ismade of a metal layer, such as copper, copper alloy, nickel, nickelalloy, aluminum, aluminum alloy, tin, tin alloy, lead, lead alloy,silver, silver alloy or a combination thereof. In some embodiments, thefirst barrier layer 144 is made of a metal layer, such as copper, copperalloy, nickel, nickel alloy, aluminum, aluminum alloy, tin, tin alloy,lead, lead alloy, silver, silver alloy or a combination thereof. In someembodiments, the first solder layer 148 is made of tin (Sn), SnAg, SnPb,SnAgCu, SnAgZn, SnZn, SnBiIn, SnIn, SnAu, SnPb, SnCu, SnZnIn, SnAgSb oranother applicable material. In some embodiments, the first pillar layer142 is made of copper (Cu), the first barrier layer 144 is made ofnickel (Ni), and the solder layer 148 is made of tin (Sn). In someembodiments, the first pillar layer 142, the first barrier layer 144 andthe first solder layer 148 are independently formed by a depositionprocess, such as an electroplating process, a physical vapor deposition(PVD) process, a chemical vapor deposition (CVD) process, or anotherapplicable process.

Afterwards, as shown in FIG. 1F, the patterned photoresist layer 135 isremoved to expose a portion of the UBM layer 130, in accordance withsome embodiments of the disclosure. In some embodiments, the patternedphotoresist layer 135 is removed by a wet etching process.

Subsequently, as shown in FIG. 1G the exposed portion of the UBM layer130, a portion of the first pillar layer 142 and a portion of the solderlayer 148 are removed, in accordance with some embodiments of thedisclosure. As a result, the first barrier layer 144 is wider than thefirst pillar layer 142 and the first solder layer 148. In someembodiments, the exposed portion of the UBM layer 130, the portion ofthe first pillar layer 142 and the portion of the solder layer 148 areremoved by a wet etching process. The wet etching solution is used toremove the UBM layer 130, a portion of the first pillar layer 142 and aportion of the solder layer 148, but not to remove the first barrierlayer 144. In other words, the etching process provides a high etchingselectivity of the UBM layer 130 and the first pillar layer 142 relativeto the first barrier layer 144. In some embodiments, the wet etchingprocess includes phosphoric acid (H₃PO₄) solution, hydrogen peroxide(H₂O₂) solution or another applicable solution.

If the first barrier layer 144 is not wider than the first pillar later142, the first solder layer 148 may flow downward, and the remindingsolder material on the first barrier layer 144 may be not enough toconnect with another bump structure, such that a short-circuit problemoccurs. When the first barrier layer 144 is wider than the first pillarlater 142, the first solder layer 148 may be prevent from flowingdownward such that the solder material is not contact with the firstpillar layer 142 and short-circuit. In order to prevent short-circuits,the first barrier layer 144 is used as a barrier structure to preventthe first solder layer 148 and other layers (such as an IMC layer,formed later, as shown in FIG. 4C) from flowing downward. Therefore, thefirst barrier layer 144 has a protruding portion 144 a which extendsaway from the sidewall surface of the first pillar layer 142.

The first pillar layer 142 has a first width W_(A) in a horizontaldirection, the first barrier layer 144 has a second width W_(B) in thehorizontal direction, and the first solder layer 148 has a third widthW_(C) in the horizontal direction. In some embodiments, the second widthW_(B) is greater than the first width W_(A). In some embodiments, thefirst width W_(A) is equal to, greater than or smaller than the thirdwidth W_(C). In some embodiments, as shown in FIG. 1G′, the first widthW_(A) is wider than the third width W_(C).

The distance D₁ between the sidewall surface of the first pillar layer142 and the sidewall surface of the first barrier layer 144 is in arange from about 0.5 μm to about 3 μm. If the distance D₁ is smallerthan 0.5 μm, the first solder layer 148 may flow downward. If thedistance D₁ is greater than 3 μm, the pitch between two adjacent firstbarrier layers 144 may be limited. Therefore, when the distance D₁ iswithin above-mentioned range, the first barrier layer 144 caneffectively prevent the first solder layer 148 from flowing downward. Insome embodiments, a ratio of the distance D₁ to the first width W_(A) isin a range from about 0.15 to about 0.4.

The first pillar layer 142 has a first height H_(A) in a verticaldirection, the first barrier layer 144 has a second height H_(B) in thevertical direction, and the first solder layer 148 has a third heightH_(C) in the vertical direction. In some embodiments, the first heightH_(A) is greater than the second height H_(B) and the third heightH_(C).

Subsequently, as shown in FIG. 1H, a reflow process is performed on thefirst solder layer 148, in accordance with some embodiments of thedisclosure. The width of the first solder layer 148 is substantiallyequal to the width of the first barrier layer 144. In addition, thereflowed first solder layer 148 has a third height Hc′. The third heightHc′ is greater than the third height H_(C).

It should be noted that the first barrier layer 144 has a protrudingportion to prevent the first solder layer 148 from flowing downward.Therefore, the reliability of the first bump structure 100 a is improvedby forming the protruding first barrier layer 144.

Furthermore, the first pillar layer 142, the first barrier layer 144 andthe first solder layer 148 are formed in the opening 137 of thephotoresist layer 135, and therefore the sidewall surfaces of the firstpillar layer 142, the sidewall surfaces of the first barrier layer 144and the sidewall surfaces of the first solder layer 148 in FIG. 1E arealigned with each other. Therefore, the misalignment problem of theselayers can be prevented. Afterwards, the width difference between thefirst pillar layer 142 and the first barrier layer 144 is fabricated byetching a portion of the first pillar layer 142 and the exposed portionof the UBM layer 130. The removal of the first pillar layer 142 and theremoval of the UBM layer 130 are performed in the same process withoutthe need for an extra etching process for removing the portion of thefirst pillar layer 142.

FIGS. 2A-2G show top views of the conductive pad 122 and the dielectriclayer 120 taken along A-A′ line of FIG. 1A, in accordance with someembodiments of the disclosure. A top-view of the conductive pad 122includes a circle (FIG. 2A), oval (FIG. 2B, square (FIG. 2C), rectangle(FIG. 2D), diamond (FIG. 2E) or polygon shape (FIG. 2F and FIG. 2G).

FIG. 3A shows a cross-sectional representation of a first bump structure100 b, in accordance with some embodiments of the disclosure. The firstbump structure 110 b is similar to the first bump structure 100 a, thedifference between FIG. 3A and FIG. 1G is that a first cap layer 146 isformed over the first barrier layer 144 in the first bump structure 110b.

The first cap layer 146 is used to form more amount of the IMC (formedlater, in FIG. 4C), and therefore the risk of the movement of the firstsolder layer 148 is reduced. The first cap layer 146 and the firstbarrier layer 144 are made of different materials. The first cap layer146 and the first pillar layer 142 may be made of a same material. Insome embodiments, the first cap layer 146 is made of a metal layer, suchas copper, copper alloy, nickel, nickel alloy, aluminum, aluminum alloy,tin, tin alloy, lead, lead alloy, silver, silver alloy or a combinationthereof. In some embodiments, the first pillar layer 142 is made ofcopper (Cu), the first barrier layer 144 is made of nickel (Ni), and thefirst cap layer 146 is made of copper. In some embodiments, the firstcap layer 146 is formed by a deposition process, such as anelectroplating process, a physical vapor deposition (PVD) process, achemical vapor deposition (CVD) process, or another applicable process.

The first cap layer 146 has a fourth width W_(D) in the horizontaldirection and a fourth height H_(D) in the vertical direction. In someembodiments, the second width W_(B) of the first barrier layer 144 isgreater than the fourth width W_(D) of the first cap layer 146. In someembodiments, the first height H_(A) of the first pillar layer 142 isgreater than the fourth height H_(D) of the first cap layer 146. Thefirst cap layer 146 has a planar top surface, and a vertical sidewallsurface.

The first cap layer 146 is formed on the first barrier layer 144, andthen a portion of the first cap layer 146 and a portion of the firstpillar layer 142 have been removed by a same wet etching process.Therefore, the first barrier layer 144 extends away from the sidewallsurface of the first pillar layer 142.

FIG. 3A′ shows a cross-sectional representation of a first bumpstructure 100 b after the reflow process, in accordance with someembodiments of the disclosure. The reflow process is performed on thefirst solder layer 148. The width of the first solder layer 148 issubstantially equal to the width of the first barrier layer 144 afterthe reflow process. In addition, the reflowed first solder layer 148 hasa third height Hc′. The third height Hc′ is greater than the thirdheight H_(C).

FIG. 3B shows a cross-sectional representation of a first bump structure100 c, in accordance with some embodiments of the disclosure. The firstbump structure 100 c is similar to the first bump structure 100 b, thedifference between FIG. 3B and FIG. 3A is that the first barrier layer144 has a convex top surface in the first bump structure 100 c.Furthermore, the first cap layer 146 is formed along the shape of thefirst barrier layer 144, and therefore the first cap layer 146 also hasa convex top surface. The first solder layer 148 also has a convex topsurface. In addition, the first barrier layer 144 has a sloped sidewallsurface. In some embodiments, the deposition parameters (electroplatingsolution, electroplating time) of the deposition process are controlledto form the convex top surface of the first barrier layer 144. In someembodiments, the convex top surface of the first barrier layer 144 isobtained by controlling the concentration, the content, and thetemperature of the electroplating solution, and controlling the currentof the plating process.

FIG. 3C shows a cross-sectional representation of a first bump structure100 d, in accordance with some embodiments of the disclosure. The firstbump structure 100 d is similar to the first bump structure 100 b, thedifference between FIG. 3C and FIG. 3A is that the first barrier layer144 has a concave top surface in the first bump structure 100 d. Thefirst cap layer 146 also has a concave top surface and the first solderlayer 148 also has a concave top surface. In some embodiments, theconcave top surface of the first barrier layer 144 is obtained bycontrolling the concentration, the content, and the temperature of theelectroplating solution, and controlling the current of the platingprocess. In addition, the first barrier layer 144 has a sloped sidewallsurface.

FIGS. 4A-4C show cross-sectional representations of various stages offorming a package structure 300, in accordance with some embodiments ofthe disclosure.

As shown in FIG. 4A, a first bump structure 100 and a second bumpstructure 200 are provided, in accordance with some embodiments of thedisclosure. The first bump structure 100 is similar to, or the same as,the second bump structure 200. The second bump structure 200 is formedover a second substrate 202. A second dielectric layer 220 is formedover the second substrate 202, and a second conductive layer 222 isformed in the second dielectric layer 220. The second bump structure 200includes a second UBM 230, a second pillar layer 242, the second barrierlayer 244, the second cap layer 246 and the second solder layer 248.Similar to the first barrier layer 144, the second barrier layer 244also has a protruding portion 244 a which extends away from the sidewallsurface of the second pillar layer 242.

Afterwards, as shown in FIG. 4B, a reflow process 500 is performed tobond the first bump structure 100 and the second bump structure 200together to form a package structure 300, in accordance with someembodiments.

In some embodiments, the reflow process is performed at a melting pointtemperature of the first solder layer 148 and/or the second solder layer248. In some embodiments, the reflow process is performed at atemperature in a range from about 100 degrees Celsius to about 300degrees Celsius. When the temperature is within above-mentioned range,the bonding quality and bonding yield are improved. However, embodimentsof the disclosure are not limited thereto. During the reflow process,the first solder layer 148 and the second solder layer 248 are meltedand reshaped to together form a solder joint 250.

Next, as shown in FIG. 4C, during the reflow process 500, a firstintermetallic compound (IMC) 152 and a second IMC 252 are formed, inaccordance with some embodiments. The first IMC 152 is between the firstcap layer 146 and the solder joint 250, and the second IMC 252 isbetween the second cap layer 246 and the solder joint 250.

The first IMC 152 and the second IMC 252 may be a substance formed whensolder comes in contact with another metal at an elevated temperature.As a result, the first IMC 152 and the second IMC 252 include solder andthe other metal (e.g., metal for forming the first cap layer 146 and thesecond cap layer 246). The first IMC 152 and the second IMC 252 haveunique mechanical and electrical properties, which are different fromthose of the solder and the other metal. In some embodiments, thesidewall surface of the first barrier layer 144 laterally extends awayfrom the sidewall surface of the first IMC 152.

The first IMC 152 and the second IMC 252 independently include materialsfrom solder and the other metal. In some embodiments, the material (suchas Sn) of the first solder layer 148 and the material (such as Cu) ofthe first cap layer 146 migrate and react with each other to form thefirst IMC 152. In some other embodiments, the material (such as Sn) ofthe first solder layer 148, the material (such as Cu) of the first caplayer 146 and the material (such as Ni) of the first barrier layer 144migrate and react with each other to form the first IMC 152. The firstIMC 152 may be referred to as an intermetallic alloy, an orderedintermetallic alloy, or a long-range-ordered alloy. The first IMC 152 isa solid-state compound containing two or more metallic elements, andexhibits metallic bonding and ordered crystal structure. In someembodiments, the first IMC 152 and the second IMC 252 independentlyinclude Cu₆Sn₅. In some other embodiments, the first IMC 152 and thesecond IMC 252 independently include Ni₃Sn₄, AuSn₄ or another suitablematerial.

FIG. 4C′ shows a cross-sectional representation of a package structure300′, in accordance with some embodiments of the disclosure. The packagestructure 300′ is similar to the package structure 300, the differencebetween FIG. 4C′ and FIG. 4C is that the solder joint 250 flows to afirst region and a second region. The first region is the sidewallsurfaces of the first cap layer 146 and/or the sidewall surfaces of thesecond cap layer 246. The second region is the top surface of the firstbarrier layer 144 and/or the bottom surface of the second barrier layer244. In some embodiments, portions of the sidewall surfaces of the firstcap layer 146 are covered by the first IMC 152. In some embodiments, aportion of the sidewall surfaces of the second cap layer 246 is coveredby the second IMC 252. A portion of the top surface of the first barrierlayer 144 is covered by the solder joint 250. A portion of the bottomsurface of the second barrier layer 244 is covered by the solder joint250.

FIGS. 5A-5J show cross-sectional representations of various stages offorming a package structure 700, in accordance with some embodiments ofthe disclosure. The package structure may be achip-on-wafer-on-substrate (CoWoS) package or another suitable package.

As shown in FIG. 5A, a first structure 10 is provided, in accordancewith some embodiments of the disclosure. The first structure 10 includesthe ILD layer 110 over the first substrate 102 and the device element104 in the ILD layer 110. The dielectric layer 120 is formed over theILD layer 110, and the conductive pad 122 formed in the dielectric layer120. The first bump structure 100 is formed over the dielectric layer120. In some embodiments, the first substrate 102 is an integratedcircuit (IC) die which is sawed from a wafer, and may be a “known gooddie”. In some embodiments, the IC die is a logic die, a memory die oranother applicable type of die.

The first bump structure 100 includes the UBM layer 130, the firstpillar layer 142, the first barrier layer 144, the first cap layer 146and the first solder layer 148. The UBM layer 130 is formed over thedielectric layer 120, and the first pillar layer 142 is formed over theUBM layer 130. The first barrier layer 144 is formed over the firstpillar layer 142, and the first cap layer 146 is formed over the firstbarrier layer 144. The first solder layer 148 is formed over the firstcap layer 146. It should be noted that the width of the first barrierlayer 144 is greater than the width of the first pillar layer 142 and/orthe width of the first cap layer 146 and/or the width of the firstsolder layer 148.

Next, as shown in FIG. 5B, a second structure 20 is provided, inaccordance with some embodiments of the disclosure. In some embodiments,the second structure 20 is an interposer. The interposer may be free ofactive elements, such as transistors, diodes or another active element.The interposer may include, or may be free of passive elements, such ascapacitors, resistors, inductors or another applicable element.

The second structure 20 includes a number of through-substrate-vias(TSVs) 210 formed in the second substrate 202. The second substrate 202includes a first surface 202 a and a second surface 202 b oppositely tothe first surface 202 a. Each of the TSVs 210 includes a conductivestructure 206 and a barrier layer 208 surrounding the conductivestructure 206. The conductive structure 206 extends from the firstsurface 202 a of the second substrate 202 towards to the second surface202 b of the second substrate 202. The dielectric layer 220 is formedover the second substrate 202, and the conductive layer 222 is formed inthe dielectric layer 220. In some embodiments, the second conductivelayer 222 is referred to redistribution layers (RDLs).

The second bump structure 200 is formed over the dielectric layer 220.The TSVs 210 are electrically connected to the second bump structure200. The second bump structure 200 includes the second UBM layer 230,the second pillar layer 242, the second barrier layer 244, the secondcap layer 246 and the second solder layer 248. The second UBM layer 230is electrically connected to the second conductive layer 222.

Next, as shown in FIG. 5C, the first structure 10 is turned upside downand placed over the second structure 20, in accordance with someembodiments of the disclosure. Afterwards, a reflow process 500 isperformed on the first bump structure 100 and the second bump structure200.

The first bump structure 100 of the first structure 10 is substantiallyaligned to the second bump structure 200 of the second structure 20. Thefirst bump structure 100 of the first structure 10 and the second bumpstructure 200 of the second structure 20 may or may not be the samesize.

Subsequently, as shown in FIG. 5D, during the reflow process 500, thefirst solder layer 148 and the second solder layer 248 are melted andreshaped to form the solder joint 250, in accordance with someembodiments of the disclosure. The first IMC 152 is formed between thefirst cap layer 146 and the solder joint 250, and the second IMC 252 isformed between the second cap layer 246 and the solder joint 250. Insome embodiments, the first IMC 152 and the second IMC 252 independentlyinclude Cu₆Sn₅. In some embodiments, the first IMC 152 and the secondIMC 252 are separated from each other by the solder joint 250. In someother embodiments, the first IMC 152 and the second IMC 252independently include Ni₃Sn₄, AuSn₄ or another suitable material.

The interface between the first IMC 152 and the solder joint 250 orbetween the second IMC 252 and the solder joint 250 may be irregular. Insome other embodiments, the interface can be observed using an electronmicroscope, such as a scanning electron microscope (SEM), and/orspectroscopy technology, such as an energy-dispersive X-ray spectroscopy(EDS, EDX or XEDS).

Afterwards, an underfill layer 260 is formed between the first structure10 and the second structure 20. The first bump structure 100, the solderjoint 250, the first IMC 152, the second IMC 252 and the secondstructure 200 are embedded in and protected by the underfill layer 260.

In some embodiments, the underfill layer 260 includes liquid epoxy,deformable gel, silicon rubber, another suitable material, or acombination thereof. In some embodiments, the underfill layer 260includes an epoxy-based resin with fillers dispersed therein. Thefillers may include insulating fibers, insulating particles, othersuitable elements, or a combination thereof. In some embodiments, adispensing and curing process is performed to form the underfill layer260.

Subsequently, as shown in FIG. 5E, the first structure 10 and the secondstructure 20, which are bonded together, are turned upside down andplaced over a carrier substrate 390, in accordance with some embodimentsof the disclosure.

In some embodiments, the carrier substrate 390 is used as a temporarysubstrate. The temporary substrate provides mechanical and structuralsupport during subsequent processing steps, such as those described inmore detail later. The carrier substrate 390 is made of a semiconductormaterial, ceramic material, polymer material, metal material, anothersuitable material, or a combination thereof. In some embodiments, thecarrier substrate 390 is a glass substrate. In some other embodiments,the carrier substrate 390 is a semiconductor substrate, such as asilicon wafer.

In some embodiments, the first structure 10 is attached to the carriersubstrate 390 through an adhesive layer (not shown). The adhesive layeris used as a temporary adhesive layer. The adhesive layer may be glue ora tape. In some embodiments, the adhesive layer is photosensitive and iseasily detached from the carrier substrate 390 by light irradiation. Forexample, shining ultra-violet (UV) light or laser light on the carriersubstrate 390 is used to detach the adhesive layer. In some embodiments,the adhesive layer is a light-to-heat-conversion (LTHC) coating. In someother embodiments, the adhesive layer is heat-sensitive and is easilydetached from the carrier substrate 390 when it is exposed to heat.

Next, as shown in FIG. 5F, the first substrate 202 of the firststructure 10 is thinned using the carrier substrate 390 as a support, inaccordance with some embodiments of the disclosure. In some embodiments,the first substrate 202 is thinned from the second surface 202 b untilthe TSVs 210 are exposed. In some embodiments, the first substrate 202is thinned by a planarization process. The planarization process mayinclude a chemical mechanical polishing (CMP) process, a grindingprocess, an etching process, another applicable process, or acombination thereof.

Afterwards, a passivation layer 270 is formed over the second substrate202, and the passivation layer 270 is patterned to form a number ofopenings. The openings expose portions of the conductive structure 206of the TSVs 210. The passivation layer 270 is made of dielectricmaterial(s) and provides stress relief for bonding stress incurredduring subsequent bonding processes. In some embodiments, thepassivation layer 270 is made of PBO, BCB, silicone, acrylates,siloxane, another suitable material, or a combination thereof. In someother embodiments, the passivation layer 270 is made of non-organicmaterials. The non-organic materials include silicon oxide, un-dopedsilicate glass, silicon oxynitride, silicon nitride, silicon carbide,HMDS, another suitable material, or a combination thereof.

Next, a number of connectors 350 are formed over the passivation layer270. The connectors 350 are electrically connected to the TSVs 210. Insome embodiments, the connectors 350 are referred to as controlledcollapse chip connection (C4) bumps. Each of the connectors 350 includesa third UBM layer 330, a third pillar layer 342, a third barrier layer344, a third cap layer 346 and a third solder layer 348.

Afterwards, as shown in FIG. 5G, the carrier substrate 390 is removed,in accordance with some embodiments of the disclosure. In someembodiments, suitable light is provided to detach the adhesive layer andlift off the carrier substrate 390.

Subsequently, a singulation process is performed to separate thewafer-level package structure 300 into multiple die-level sub-packagestructures 400. One of the sub-package structures 400 is shown in FIG.5G. In some embodiments, the singulation process is a dicing process.

Afterwards, as shown in FIG. 5H, the sub-package structure 400 is bondedto a third substrate 602 through the connectors 350, in accordance withsome embodiments of the disclosure. In some embodiments, the thirdsubstrate 602 is a printed circuit board (PCB), a ceramic substrate oranother suitable package substrate. Next, a reflow process 550 isperformed on the sub-package structures 400 and the third substrate 602to form a package structure 700.

Afterwards, as shown in FIG. 5I, an underfill layer 660 is formedbetween the sub-package structures 400 and the third substrate 602, inaccordance with some embodiments of the disclosure. As a result, theconnectors 350 are embedded in and protected by the underfill layer 660.Next, a number of connectors 670 are formed on a bottom surface of thethird substrate 602. The connectors 670 are electrically connected tothe connectors 350 and the sub-package 400.

As shown in FIG. 5I, a first pitch P₁ is between two adjacent firstpillar layers 142, a second pitch P₂ is between two adjacent thirdpillar layers 342, and a third pitch P₃ is between two adjacentconnectors 670. In some embodiments, the first pitch P₁ is in a rangefrom about 30 μm to about 60 μm. In some embodiments, the second pitchP₂ is in a range from about 100 μm to about 300 μm. In some embodiments,the third pitch P₃ is in a range from about 800 μm to about 1000 μm.

Subsequently, as shown in FIG. 5J, a test 750 is performed on thepackage structure 700, in accordance with some embodiments of thedisclosure.

In some embodiments, the test 750 is a high-temperature storage (HTS)test, a temperature cycling test (TCT), or another suitablequalification test. The HTS test may be complied with JEDEC (JointElectron Device Engineering Council) standards. In some embodiments, thetest 750 is performed at about 150 degrees Celsius, but embodiments ofthe disclosure are not limited thereto. In some embodiments, theoperation time of the test 750 is in a range from about 1000 hours toabout 3000 hours. For example, the operation time of the test 750 may beabout 1500 hours. However, embodiments of the disclosure are not limitedthereto.

It should be noted that the first solder layer 148 and the second solderlayer 248 may flow or migrate as the using time of the package structure700 is increased. If no protruding first barrier layer 144 is formed,the first solder layer 148 may flow downward to make contact with thefirst pillar layer 142 causing a short-circuit. In order to preventshort-circuits, the first barrier layer 144 and the second barrier layer244 are designed to have a wider width to provide a barrier wall.

The package structure includes the first bump structure bonded to thesecond bump structure. The first barrier layer has the protrudingportion to block portions of the first solder layer which may flow whenthe using time of the package structure is increased. In other words,the first barrier layer is used to prevent the first solder layer fromcontacting the first pillar layer.

Embodiments for forming a package structure and method for forming thesame are provided. A first package structure including a first bumpstructure is bonded to a second package structure including a secondbump structure. The first bump structure includes a first pillar layer,a first barrier layer over the first pillar layer. The first barrierlayer has a protruding portion which extends away from the sidewallsurface of the first pillar layer. The second bump structure is similarto the second bump structure and has a second barrier layer. The firstbump structure is boned to the second bump structure to form a firstIMC, a solder joint and a second IMC. The first barrier layer has awider width to prevent the first solder layer from contacting the firstpillar layer. Therefore, the performance and reliability of the packagestructure is improved.

In some embodiments, a package structure is provided. The packagestructure includes a first bump structure formed over a substrate, asolder joint formed over the first bump structure and a second bumpstructure formed over the solder joint. The first bump structureincludes a first pillar layer formed over the substrate and a firstbarrier layer formed over the first pillar layer. The first barrierlayer has a protruding portion which extends away from a sidewallsurface of the first pillar layer, and a distance between the sidewallsurface of the first pillar layer and a sidewall surface of the firstbarrier layer is in a range from about 0.5 μm to about 3 μm. The secondbump structure includes a second barrier layer formed over the solderjoint and a second pillar layer formed over the second barrier layer.The second barrier layer has a protruding portion which extends awayfrom a sidewall surface of the second pillar layer.

In some embodiments, a package structure is provided. The packagestructure includes a first structure formed over a first substrate. Thefirst structure includes a first bump structure, the first bumpstructure includes a first pillar layer formed over the first substrate,and the first pillar layer has a first width in a horizontal direction.The first bump structure further includes a first barrier layer formedover the first pillar layer, and the first barrier layer has a secondwidth in the horizontal direction, and the second width is greater thanthe first width. The first bump structure further includes a first caplayer formed over the first barrier layer, the first cap layer has athird width in the horizontal direction, and the second width is greaterthan the third width. The package structure also includes a first interintermetallic compound (IMC) over the first bump structure, and aportion of a top surface of the first barrier layer is covered by thefirst IMC. A sidewall surface of the first pillar layer is free of firstIMC. The package structure further includes a solder joint formed overthe first IMC and a second structure formed over the solder joint.

In some embodiments, a method for forming a package structure isprovided. The method includes forming an under bump metallization (UBM)layer over a metal pad and forming a photoresist layer over the UBMlayer. The method also includes patterning the photoresist layer to forman opening in the photoresist layer, and a first portion of the UBMlayer is exposed by the opening. The method further includes forming afirst bump structure over the first portion of the UBM layer. The firstbump structure includes a first barrier layer over a first pillar layer,and a width of the first barrier layer is greater than a width of thefirst pillar layer. The method also includes placing a second bumpstructure over the first bump structure, and the second bump structureincludes a second barrier layer over a second pillar layer, and a widthof the second barrier layer is greater than a width of the second pillarlayer. The method further includes reflowing the first bump structureand the second bump structure to form a solder joint, a first interintermetallic compound (IMC) and a second IMC, and the solder joint isbetween the first IMC and the second IMC.

In some embodiments, forming the first bump structure over the firstportion of the UBM layer includes: forming the first pillar layer in theopening over the first portion of the UBM layer; forming the firstbarrier layer over the first pillar layer; forming a solder layer overthe first barrier layer; removing the patterned photoresist layer toexpose a second portion of the UBM layer; and removing the secondportion of the UBM layer, a portion of the first pillar layer and aportion of the solder layer, such that the first barrier layer has aprotruding portion which extends away from a sidewall surface of thefirst pillar layer.

In some embodiments, the method further includes: forming a first caplayer over the first barrier layer, and removing a portion of the firstcap layer while removing the second portion of the UBM layer, theportion of the first pillar layer and the portion of the solder layer.

In some embodiments, forming the first bump structure further includesforming an interface between the first cap layer and the first barrierlayer, and the interface is a planar surface, a concave surface or aconvex surface.

In some embodiments, a width of the solder layer is greater than a widthof the first cap layer after the portion of the first cap layer isremoved.

In some embodiments, reflowing the first bump structure and the secondbump structure further includes forming a first portion of the solderjoint over the first IMC and a second portion of the solder jointadjacent to the first cap layer. The first portion and the secondportion are separated by the first IMC.

In some embodiments, forming the solder joint further includes makingthe solder joint free of a top surface of the first barrier layer.

In some embodiments, a method for forming a package structure isprovided. The method includes forming a first structure over a firstsubstrate. Forming the first structure includes forming a first bumpstructure, and forming the first bump structure includes: forming afirst pillar layer over the first substrate; forming a first barrierlayer over the first pillar layer; and forming a first cap layer overthe first barrier layer. The method also includes placing a secondstructure over the first bump structure. The second structure includes asecond bump structure. The method further includes reflowing the firstbump structure and the second bump structure to form a solder joint anda first inter intermetallic compound (IMC). The first IMC is formed overthe first cap layer. The solder joint includes a first portion formedover the first IMC and a second portion adjacent to the first cap layeron the top surface of the first barrier layer. The first portion and thesecond portion are separated by the first IMC.

In some embodiments, reflowing the first bump structure and the secondstructure further includes forming a second IMC, the second IMC iscloser to the second bump structure than the first IMC.

In some embodiments, forming the first bump structure further includes:forming the first pillar layer with a first width in a horizontaldirection; and forming the first barrier layer with a second width inthe horizontal direction. The second width is greater than the firstwidth.

In some embodiments, forming the first bump structure further includes:forming the first cap layer with a third width in the horizontaldirection. The second width is greater than the third width.

In some embodiments, the method further includes providing a pluralityof through-substrate-vias (TSV) formed in a second substrate. The TSVsare electrically connected to the second bump structure.

In some embodiments, the method further includes forming a plurality ofconnectors over the second structure. The connectors are electricallyconnected to the TSVs. The method further includes forming au underfilllayer. The connectors are embedded in the underfill layer.

In some embodiments, forming the first bump structure further includes:forming the first pillar layer with a first height in a verticaldirection; forming the first barrier layer with a second height in thevertical direction; and forming the first cap layer with a third heightin the vertical direction. The first height is greater than the secondheight and the third height.

In some embodiments, a method for forming a package structure isprovided. The method includes forming a first structure over a firstsubstrate. Forming the first structure includes forming a first bumpstructure, and forming the first bump structure includes: forming afirst pillar layer over the first substrate. The first pillar layer hasa first width in a horizontal direction; and forming a first barrierlayer over the first pillar layer. The first barrier layer has a secondwidth in the horizontal direction, and the second width is greater thanthe first width. The method further includes placing a second structureover the first bump structure. The second structure includes a secondbump structure. The method also includes reflowing the first bumpstructure and the second bump structure to form a solder joint. Thesolder joint is formed to be electrically connected to the first bumpstructure and the second structure, and a top surface of the firstbarrier layer without vertically overlapping the first pillar layer isfree of the solder joint.

In some embodiments, forming the second bump structure further includes:forming a second pillar layer formed over a second substrate. The secondpillar layer has a third width in the horizontal direction. The methodalso includes forming a second barrier layer formed over the secondpillar layer. The second barrier layer has a fourth width in thehorizontal direction, and the fourth width is greater than the thirdwidth.

In some embodiments, reflowing the first bump structure and the secondbump structure further comprising forming a first inter intermetalliccompound (IMC) over the first bump structure, and a width of the firstIMC is less than the second width of the first barrier layer in thehorizontal direction.

In some embodiments, forming the first bump structure further includes:forming an interface between the first piller layer and the firstbarrier layer, and the interface is a planar surface, a concave surfaceor a convex surface.

In some embodiments, forming the first bump structure further includes:forming a first solder layer over the first barrier layer; removing aportion of the first solder layer; and reflowing the first solder layer.A width of the reflowed first solder layer is substantially equal to thesecond width of the first barrier layer in the horizontal direction.

In some embodiments, forming the first bump structure further includes:forming a first cap layer over the first barrier layer; and removing aportion of the first cap layer while removing a portion of the firstpillar layer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for forming a package structure,comprising: forming an under bump metallization (UBM) layer over a metalpad; forming a photoresist layer over the UBM layer; patterning thephotoresist layer to form an opening in the photoresist layer, wherein afirst portion of the UBM layer is exposed by the opening; forming afirst bump structure over the first portion of the UBM layer, whereinthe first bump structure comprises a first barrier layer over a firstpillar layer, and a width of the first barrier layer is greater than awidth of the first pillar layer; placing a second bump structure overthe first bump structure, wherein the second bump structure comprises asecond barrier layer over a second pillar layer, and a width of thesecond barrier layer is greater than a width of the second pillar layer;and reflowing the first bump structure and the second bump structure toform a solder joint, a first inter intermetallic compound (IMC) and asecond IMC, wherein the solder joint is between the first IMC and thesecond IMC.
 2. The method for forming the package structure as claimedin claim 1, wherein forming the first bump structure over the firstportion of the UBM layer comprises: forming the first pillar layer inthe opening over the first portion of the UBM layer; forming the firstbarrier layer over the first pillar layer; forming a solder layer overthe first barrier layer; removing the patterned photoresist layer toexpose a second portion of the UBM layer; and removing the secondportion of the UBM layer, a portion of the first pillar layer and aportion of the solder layer, such that the first barrier layer has aprotruding portion which extends away from a sidewall surface of thefirst pillar layer.
 3. The method for forming the package structure asclaimed in claim 2, further comprising: forming a first cap layer overthe first barrier layer; and removing a portion of the first cap layerwhile removing the second portion of the UBM layer, the portion of thefirst pillar layer and the portion of the solder layer.
 4. The methodfor forming the package structure as claimed in claim 3, wherein formingthe first bump structure further comprises forming an interface betweenthe first cap layer and the first barrier layer, and the interface is aplanar surface, a concave surface or a convex surface.
 5. The method forforming the package structure as claimed in claim 3, wherein a width ofthe solder layer is greater than a width of the first cap layer afterthe portion of the first cap layer is removed.
 6. The method for formingthe package structure as claimed in claim 3, wherein reflowing the firstbump structure and the second bump structure further comprises forming afirst portion of the solder joint over the first IMC and a secondportion of the solder joint adjacent to the first cap layer, wherein thefirst portion and the second portion are separated by the first IMC. 7.The method for forming the package structure as claimed in claim 1,wherein forming the solder joint further comprises making the solderjoint free of a top surface of the first barrier layer.
 8. A method forforming a package structure, comprising: forming a first structure overa first substrate, wherein forming the first structure comprises forminga first bump structure, and forming the first bump structure comprises:forming a first pillar layer over the first substrate; forming a firstbarrier layer over the first pillar layer; and forming a first cap layerover the first barrier layer; placing a second structure over the firstbump structure, wherein the second structure comprises a second bumpstructure; and reflowing the first bump structure and the second bumpstructure to form a solder joint and a first inter intermetalliccompound (IMC), wherein the first IMC is formed over the first caplayer, wherein the solder joint comprises a first portion formed overthe first IMC and a second portion adjacent to the first cap layer onthe top surface of the first barrier layer, wherein the first portionand the second portion are separated by the first IMC.
 9. The method forforming the package structure as claimed in claim 8, wherein reflowingthe first bump structure and the second structure further comprisesforming a second IMC, the second IMC is closer to the second bumpstructure than the first IMC.
 10. The method for forming the packagestructure as claimed in claim 8, wherein forming the first bumpstructure further comprises: forming the first pillar layer with a firstwidth in a horizontal direction; and forming the first barrier layerwith a second width in the horizontal direction, wherein the secondwidth is greater than the first width.
 11. The method for forming thepackage structure as claimed in claim 10, wherein forming the first bumpstructure further comprises: forming the first cap layer with a thirdwidth in the horizontal direction, wherein the second width is greaterthan the third width.
 12. The method for forming the package structureas claimed in claim 8, further comprising providing a plurality ofthrough-substrate-vias (TSV) formed in a second substrate, wherein theTSVs are electrically connected to the second bump structure.
 13. Themethod for forming the package structure as claimed in claim 12, furthercomprising: forming a plurality of connectors over the second structure,wherein the connectors are electrically connected to the TSVs; andforming au underfill layer, wherein the connectors are embedded in theunderfill layer.
 14. The method for forming the package structure asclaimed in claim 8, wherein forming the first bump structure furthercomprises: forming the first pillar layer with a first height in avertical direction; forming the first barrier layer with a second heightin the vertical direction; and forming the first cap layer with a thirdheight in the vertical direction, wherein the first height is greaterthan the second height and the third height.
 15. A method for forming apackage structure, comprising: forming a first structure over a firstsubstrate, wherein forming the first structure comprises forming a firstbump structure, and forming the first bump structure comprises: forminga first pillar layer over the first substrate, wherein the first pillarlayer has a first width in a horizontal direction; and forming a firstbarrier layer over the first pillar layer, wherein the first barrierlayer has a second width in the horizontal direction, and the secondwidth is greater than the first width; placing a second structure overthe first bump structure, wherein the second structure comprises asecond bump structure; and reflowing the first bump structure and thesecond bump structure to form a solder joint, wherein the solder jointis formed to be electrically connected to the first bump structure andthe second structure, and a top surface of the first barrier layerwithout vertically overlapping the first pillar layer is free of thesolder joint.
 16. The method for forming the package structure asclaimed in claim 15, wherein forming the second bump structure furthercomprises: forming a second pillar layer formed over a second substrate,wherein the second pillar layer has a third width in the horizontaldirection; and forming a second barrier layer formed over the secondpillar layer, wherein the second barrier layer has a fourth width in thehorizontal direction, and the fourth width is greater than the thirdwidth.
 17. The method for forming the package structure as claimed inclaim 15, wherein reflowing the first bump structure and the second bumpstructure further comprising forming a first inter intermetalliccompound (IMC) over the first bump structure, and a width of the firstIMC is less than the second width of the first barrier layer in thehorizontal direction.
 18. The method for forming the package structureas claimed in claim 15, wherein forming the first bump structure furthercomprises: forming an interface between the first piller layer and thefirst barrier layer, and the interface is a planar surface, a concavesurface or a convex surface.
 19. The method for forming the packagestructure as claimed in claim 15, wherein forming the first bumpstructure further comprises: forming a first solder layer over the firstbarrier layer; removing a portion of the first solder layer; andreflowing the first solder layer, wherein a width of the reflowed firstsolder layer is substantially equal to the second width of the firstbarrier layer in the horizontal direction.
 20. The method for formingthe package structure as claimed in claim 15, wherein forming the firstbump structure further comprises: forming a first cap layer over thefirst barrier layer; and removing a portion of the first cap layer whileremoving a portion of the first pillar layer.